The invention relates to breaking ice, and more particularly to breaking ice by discharging substantial quantities of water onto the surface of the ice.
Since the discovery of petroleum in the Arctic regions of North America, efforts have begun to develop means for transporting the petroleum to processing and marketing areas in the more temperate climates. Two methods have been proposed; pipelines and tankers. At present only pipelines are being considered due to the difficulty of moving tankers through the ice that covers much of the Arctic oceans.
A notable effort to prove the feasibility of tankers for use in Arctic areas was made in the voyage in 1969 of the S.S. Manhattan through the Northwest Passage. Arctic Oil and the S.S. Manhattan, 2 UMR Journal 67, (1971). The Manhattan combined the principles of the tanker and the ice breaker in one vessel.
The conventional ice breaker concept is well-known. An ice breaker breaks ice by using two forces in combination. Initially, the ice breaker rams a sheet of ice, breaking what it can by the force of the impact. If the sheet remains, the ice breaker rides up onto the top of the sheet and breaks it by the downward force of its weight.
Some ice breakers use auxiliary means to assist them. Saws to cut grooves ahead of an ice breaker to weaken the ice are disclosed in U.S. Pat. No. 3,632,172 to Robinson; and explosives are utilized in U.S. Pat. No. 3,572,273 to Wood. Fluids are also used in several patents. U.S. Pat. No. 3,530,814 to Rastorguev et al discloses an ice breaker that includes a vibratory mechanism to impart vibrations into the ice and a washoff system through which water jets are directed to drive the submerged broken ice beyond the ice land to a safe distance. British Pat. No. 21,844 discloses an ice breaker equipped with steam heaters that direct heated water toward the bow propeller to assist in dissolving "frazil" ice. British Pat. No. 20,536 illustrates an ice breaker equipped with nozzles for discharging compressed air to remove snow from the path of the ship.
Conventional ice breakers, however, as evidenced by the experience of the Manhattan are not effective against the ice of the Arctic oceans. There are two significant problems. First, ice breakers are inefficient, only about 15% of the total energy expended being used to break ice. About 80% is lost to friction. The Manhattan attempted to alleviate this friction by using heat in the hull to provide a layer of water as lubrication. Second, ice breakers have poor manueverability due to the narrow path broken through the ice. If an ice breaker of the Manhattan type were to encounter unbreakable ice, its only choices would be to move backwards or to seek help from other ice breakers.
This is also a problem even before the ship encounters ice it cannot break. In heavy ice the ship may still be able to proceed slowly forward in a straight line, but cannot change course because the channel it cuts is too narrow.